1. Field of the Invention
This invention relates to a chair backrest elevating device, particularly to one having a slide base and a slide cover assembled on a chair backrest, and a fixing plate unit combined with a chair seat. Thus, when the chair backrest is pulled up or down, the slide base and the slide cover will be actuated to shift to enable the sustaining member of an adjusting unit, which is combined with the positioning rod of the slide base, to be correspondingly engaged and positioned in different-level engage grooves of an engage block, thus attaining effect of adjusting a chair backrest to move upward or downward.
2. Description of the Prior Art
Generally, the seat and the backrest of a conventional chair are fixed in form and impossible to be adjusted, while the backrest of another conventional chair is adjustable in elevation angles so that a user can lie on the backrest comfortably. However, the backrests of these two conventional chairs are respectively secured at the rear side of the seat and fixed in height; therefore, the backrest is impossible to be adjusted in height for matching with the height and the stature of a sitter in order to effectively support the back of the sitter.